Bumper-reinforcing system for motor vehicle

1. A bumper-reinforcing system for a motor vehicle, the bumper-reinforcing system comprising:

a bumper beam with a single-piece elongated profile with a closed cross section and including a center zone extending at least over part of a width of the bumper beam and an end zone at each extremity of the bumper beam;

two bumper fasteners connected to a rear side of the bumper beam at intersections between the center zone and the end zones of the bumper beam; two front rails connected to the bumper fasteners and two suspension arm brackets extending outwardly from the front rails;

two reinforcing tubes connected by a respective first end to the rear side of the bumper beam at a respective end zone, the reinforcing tubes extending from the bumper beam so as to form an angle α below 45° with a vertical plane of symmetry of the bumper beam and suited to be connected by an other end on a respective front rail of the front rails, the front rails being provided for the bumper-reinforcing system; and

two covers with a single-piece elongated profile with an open cross section, in contact with the rear side of the bumper beam at the end zones and extending at least from the first end of one of the reinforcing tubes to one of the bumper fasteners,

the reinforcing tubes being connected by the other end at a junction of the respective front rail of the front rails and a respective suspension arm bracket of the suspension arm brackets,

the front rail comprising a front part made of steel having a tensile strength comprised between 450 and 1150 MPa and a total elongation above 8% and a rear part made of a fully martensitic steel, obtained by press hardening, with a tensile strength comprised between 1400 and 2000 MPa and a carbon content comprised between 0.15 and 0.5 wt %.

2. A bumper-reinforcing system for a motor vehicle, the bumper-reinforcing system comprising:

a bumper beam with a single-piece elongated profile with a closed cross section and including a center zone extending at least over part of a width of the bumper beam and an end zone at each extremity of the bumper beam;

two bumper fasteners connected to a rear side of the bumper beam at intersections between the center zone and the end zones of the bumper beam; two front rails connected to the bumper fasteners and two suspension arm brackets extending outwardly from the front rails;

two reinforcing tubes connected by a respective first end to the rear side of the bumper beam at a respective end zone, the reinforcing tubes extending from the bumper beam so as to form an angle α below 45° with a vertical plane of symmetry of the bumper beam and suited to be connected by an other end on a respective front rail of the front rails, the front rails being provided for the bumper-reinforcing system; and

two covers with a single-piece elongated profile with an open cross section, in contact with the rear side of the bumper beam at the end zones and extending at least from the first end of one of the reinforcing tubes to one of the bumper fasteners,

the reinforcing tubes being connected by the other end at a junction of the respective front rail of the front rails and a respective suspension arm bracket of the suspension arm brackets.

3. The bumper-reinforcing system as recited in claim 2 wherein the reinforcing tubes do not protrude from an end of the bumper beam in a longitudinal direction of the bumper beam.

4. The bumper-reinforcing system as recited in claim 2 wherein the reinforcing tubes are made of a dual-phase steel with a tensile strength between 780 and 900 MPa.

5. The bumper-reinforcing system as recited in claim 2 wherein the reinforcing tubes are hollow tubes having a circular cross section.

6. The bumper-reinforcing system as recited in claim 2 wherein the bumper beam has a B-shaped cross section.

7. The bumper-reinforcing system as recited in claim 2 wherein the bumper beam comprises a web and two legs extending perpendicularly from the web.

8. The bumper-reinforcing system as recited in claim 2 wherein the bumper beam is made of a fully martensitic steel with a tensile strength between 1500 and 1900 MPa.

9. The bumper-reinforcing system as recited in claim 2 wherein the covers have a U-shaped cross section.

10. The bumper-reinforcing system as recited in claim 9 wherein the covers comprise a web and two legs extending perpendicularly from the web.

11. The bumper-reinforcing system as recited in claim 10 wherein the bumper beam comprises a bumper web and two bumper legs extending perpendicularly from the bumper web, and wherein the legs of the cover are in contact with the bumper legs and the web of the cover is in contact with the bumper web.

12. The bumper-reinforcing system as recited in claim 2 wherein the covers extend beyond the bumper fasteners.

13. The bumper-reinforcing system as recited in claim 2 wherein the covers extend up to an extremity of the bumper beam.

14. The bumper-reinforcing system as recited in claim 2 wherein the covers are made of a dual-phase steel with a tensile strength between 1180 and 1320 MPa.

15. A motor vehicle body structure comprising:

the bumper-reinforcing system as recited in claim 2 .

16. A motor vehicle comprising:

the bumper-reinforcing system as recited in claim 2 .